optabs: ensure atomic_load/stores have compiler barriers

	PR rtl-optimization/57448
	PR target/67458
	PR target/81316
	* optabs.c (expand_atomic_load): Place compiler memory barriers if
	using atomic_load pattern.
	(expand_atomic_store): Likewise.
testsuite/
	* gcc.dg/atomic/pr80640-2.c: New testcase.
	* gcc.dg/atomic/pr81316.c: New testcase.

From-SVN: r251643

gcc/ChangeLog

+2017-09-04  Alexander Monakov  <amonakov@ispras.ru>
+
+	PR rtl-optimization/57448
+	PR target/67458
+	PR target/81316
+	* optabs.c (expand_atomic_load): Place compiler memory barriers if
+	using atomic_load pattern.
+	(expand_atomic_store): Likewise.
+
 2017-09-04  Jakub Jelinek  <jakub@redhat.com>
 
 	PR sanitizer/81981

gcc/optabs.c

@@ -6344,12 +6344,20 @@ expand_atomic_load (rtx target, rtx mem, enum memmodel model)
   if (icode != CODE_FOR_nothing)
     {
       struct expand_operand ops[3];
+      rtx_insn *last = get_last_insn ();
+      if (is_mm_seq_cst (model))
+	expand_asm_memory_barrier ();
 
       create_output_operand (&ops[0], target, mode);
       create_fixed_operand (&ops[1], mem);
       create_integer_operand (&ops[2], model);
       if (maybe_expand_insn (icode, 3, ops))
-	return ops[0].value;
+	{
+	  if (!is_mm_relaxed (model))
+	    expand_asm_memory_barrier ();
+	  return ops[0].value;
+	}
+      delete_insns_since (last);
     }
 
   /* If the size of the object is greater than word size on this target,
@@ -6394,11 +6402,19 @@ expand_atomic_store (rtx mem, rtx val, enum memmodel model, bool use_release)
   icode = direct_optab_handler (atomic_store_optab, mode);
   if (icode != CODE_FOR_nothing)
     {
+      rtx_insn *last = get_last_insn ();
+      if (!is_mm_relaxed (model))
+	expand_asm_memory_barrier ();
       create_fixed_operand (&ops[0], mem);
       create_input_operand (&ops[1], val, mode);
       create_integer_operand (&ops[2], model);
       if (maybe_expand_insn (icode, 3, ops))
-	return const0_rtx;
+	{
+	  if (is_mm_seq_cst (model))
+	    expand_asm_memory_barrier ();
+	  return const0_rtx;
+	}
+      delete_insns_since (last);
     }
 
   /* If using __sync_lock_release is a viable alternative, try it.

gcc/testsuite/ChangeLog

+2017-09-04  Alexander Monakov  <amonakov@ispras.ru>
+
+	PR rtl-optimization/57448
+	PR target/67458
+	PR target/81316
+	* gcc.dg/atomic/pr80640-2.c: New testcase.
+	* gcc.dg/atomic/pr81316.c: New testcase.
+
 2017-09-04  Tom de Vries  <tom@codesourcery.com>
 
 	PR tree-optimization/82052

gcc/testsuite/gcc.dg/atomic/pr80640-2.c

+/* { dg-do run } */
+/* { dg-options "-pthread" } */
+/* { dg-require-effective-target pthread } */
+
+#include <pthread.h>
+
+static volatile int sem1;
+static _Atomic  int sem2;
+
+static void *f(void *va)
+{
+  void **p = va;
+  if (*p) return *p;
+  sem1 = 1;
+  while (!__atomic_load_n(&sem2, __ATOMIC_ACQUIRE));
+  // GCC used to RTL-CSE this and the first load, causing 0 to be returned
+  return *p;
+}
+
+int main()
+{
+  void *p = 0;
+  pthread_t thr;
+  if (pthread_create(&thr, 0, f, &p))
+    return 2;
+  while (!sem1);
+  __atomic_thread_fence(__ATOMIC_ACQUIRE);
+  p = &p;
+  __atomic_store_n(&sem2, 1, __ATOMIC_RELEASE);
+  pthread_join(thr, &p);
+  return !p;
+}

gcc/testsuite/gcc.dg/atomic/pr81316.c

+/* { dg-do run } */
+/* { dg-options "-pthread" } */
+/* { dg-require-effective-target pthread } */
+
+#include <pthread.h>
+#include <stdlib.h>
+
+static _Atomic int sem1;
+
+static void *f(void *va)
+{
+  void **p = va;
+  while (!__atomic_load_n(&sem1, __ATOMIC_ACQUIRE));
+  exit(!*p);
+}
+
+int main(int argc)
+{
+  void *p = 0;
+  pthread_t thr;
+  if (pthread_create(&thr, 0, f, &p))
+    return 2;
+  // GCC used to RTL-DSE this store
+  p = &p;
+  __atomic_store_n(&sem1, 1, __ATOMIC_RELEASE);
+  int r = -1;
+  while (r < 0) asm("":"+r"(r));
+  return r;
+}